1. Field of the Invention
The present invention relates to a novel process for producing tofu (bean curd).
2. Description of the Related Art
Tofu is roughly divided into two types, momen (pressed) tofu and silken tofu. Silken tofu is further divided according to the process of preparation into (1) cut tofu which is obtained by coagulating soybean milk in a mold and immersing the coagulated product in water, cutting to size and (2) packed tofu which is obtained by filling a small container of given size with soybean milk containing a coagulant, sealing the container, and coagulating by heat. In a traditional manner, both momen tofu and silken tofu are prepared by pouring hot soybean milk just squeezed out into a mold, mixing natural coagulants such as MgCl.sub.2 and CaCl.sub.2 into the soybean milk and stirring, and allowing the mixture to stand to completely coagulate. In preparing momen tofu, the coagulated product in the mold is collapsed and transferred into a wooden draining frame with cloth lying therein, then pressed to drain part of contained water and shaped. The resulting tofu is then cut to size and immersed in water. In preparing silken tofu, coagulation is completed within the mold, and the resulting tofu is cut to size and immersed in water.
Nowadays packed tofu predominates over cut tofu from the standpoint of practicability for mass production, convenience in distribution, hygiene, and so forth.
Packed tofu is generally produced by filling a container with cold soybean milk containing a coagulant, sealing the container, and coagulating the soybean milk by heating. On the other hand, there have been proposed a process comprising passing soybean milk through a pipe while causing coagulation by heating and continuously extruding the thus coagulated product from the pipe (see Japanese Patent Laid-Open No. 322731/97) and a process comprising passing soybean milk containing a coagulant through a microwave heating apparatus at a speed that may not coagulate the soybean milk, while microwave heating at 110 to 120.degree. C. for 12 to 20 seconds, and packing the still fluid soybean milk in an arbitrary mold container where the soybean milk is coagulated (see Japanese Patent Laid-Open No. 51865/83).
Quality of tofu consists in not only flavor but texture. A desirable texture depends on whether tofu is to be served as a cooked dish or to be tasted just as warmed or chilled.
While the texture of tofu varies according to the raw soybeans, the method for preparing soybean milk, the protein concentration of soybean milk, the kind and amount of the coagulant, and the like, the texture of tofu prepared in the above-described traditional method can be seen as being decided by the degree of agitation after addition of a coagulant to hot soybean milk. Therefore, tofu prepared by many tofu makers in a traditional manner can naturally have as many textures, namely, on a one-of-a-kind basis.
On the other hand, although packed tofu is advantageous in that a product of a kind can be mass-produced in a continuous manner, it is said to be inferior in texture, which has been one of the reasons of consumers' dislike for packed tofu. While the texture is influenced by such conditions as the method for preparing soybean milk, the protein concentration, the kind of the coagulant, and the like as mentioned above, it is extremely difficult to vary the texture of packed tofu according to the way of serving (e.g., whether to be cooked or to be served chilled or warmed) simply by somewhat altering these conditions. In other words, the greatest decisive factor of the texture of packed tofu resides in the mode of coagulation which consists of heat-coagulating soybean milk as packed in a container.